It is known to provide blades with lightning protection systems to protect them from strokes of lightning. As an example, WO 96/07825 discloses a lightning protection system, in which the blade tip is provided with a so-called lightning receptor of an electrically conductive material. This lightning receptor can “capture” a stroke of lightning and conduct the current through a lightning conductor downwards, said conductor extending in the longitudinal direction of the blade and being earthed via the hub. This system has proved to provide a particularly effective protection.
However, there is a risk of a flashover or sparkover from the lightning receptor or lightning conductor to pools of water on the blade, since water is electrically conductive. In this case, lightning current heats up the water, which may cause a “steam explosion”. This may result in pressure increases sufficiently high to damage the blade. Flashovers may also occur because of deposits of, for example, particles from the air, salts or insects on the blade surfaces. The damages due to flashovers result in the blade having to be repaired or, in the worst case, exchanged, which is a time-consuming and expensive process, since carrying out repairs or blade exchanges is complicated, especially for offshore wind power plants.
Moreover, providing a lightning receptor and a lightning conductor in blades made of carbon fibres is problematic, as carbon fibres are typically electrically conductive as well.
The object of the invention is to provide a new and improved lightning protection arrangement for wind power plants.